In same saucepan, in 1 tablespoon olive oil, cook onion over medium heat until tender, about 7 minutes. Add rice and 3/4 teaspoon salt and cook, stirring frequently, until rice grains are opaque. Add wine; cook until absorbed. Add about 1/2 cup simmering broth to rice, stirring until liquid is absorbed. Continue cooking, adding remaining broth, 1/2 cup at a time, and stirring after each addition until all liquid is absorbed and rice is tender but still firm, about 25 minutes (risotto should have a creamy consistency). Stir in vegetables, Parmesan, and basil; heat through.